1. Field of the Invention
The invention relates to a process and apparatus for automatically taking advantage of Kohler's Principle of Illumination in microscopes having a variable magnification system as well as an illumination system.
2. Description of the Prior Art
In the generation of a microscopic image the aperture and correction of the imaging optics determine the power of resolution as well as the contrast. However, the highest resolution and best contrast are obtainable only by using an optimally adapted and correctly adjusted illumination system. In such a system illumination of the object is required which completely and uniformly illuminates the field of vision covered by the objective used with an aperture still acceptable by the objective, i.e., an aperture resulting in an optimum ratio between resolution and contrast.
The simplest manner for obtaining this type of illumination has entailed using a collector and a condenser, both having constant focal length.
When using microscopes having variable magnification, collectors and condensers are designed for the largest possible field of vision and the largest possible aperture. Nevertheless, because the field of vision to be illuminated and the aperture required vary with each change of the objective, the illumination must be correspondingly adapted by means of diaphragms arranged in the planes of the field of view and the aperture so as to avoid, for example, a reduction in image contrast through over-illumination. Such an arrangement is disadvantageous, since in most cases the total potential optical conductance of the illumination system cannot be fully utilized.
For this reason, it has previously been proposed to provide illumination systems with variable focal lengths in order to be able to contain continuous variation of the field of vision and of the aperture. Yet, even though such a system makes it possible to adapt the field of vision and the aperture to the objective being used, while at the same time taking advantage of the total optical conductance, the fact that various adjustments must be made manually is a disadvantage. Such an apparatus involves time consuming adjustment because of the accuracy and care involved in properly setting the device. Additionally, the final results depend to a great extent on the alertness and skill of the operator. The disadvantage of such a system becomes readily apparent when performing reproducible comparative observations.
In an attempt to overcome the above disadvantages, German Auslegeschrift No. 2,219,521 discloses an adjustment drive which connects the adjustable illumination system with the objective changing device. The drive is controlled by scanning elements arranged on the objective changing device and/or on the objectives themselves.
However, the equipment necessarily involved with such a device as well as the additional time and care necessary for the alignment of additional objectives to be set into the changing device makes such a system undesirable.